A workpiece, such as a log or a cant, having a maximum of 30 inches in diameter is typically transported on a sharp chain conveyor system. This is also typically known as a “Single Length Infeed” (SLI) system. Such a sharp chain conveyor system includes a conveyor chain having sharp teeth which extend vertically upwards from the conveyor chain to firmly engage and secure onto the surface of the workpiece. A plurality of parallel spaced apart turning rolls are perpendicular to the direction of flow of the sharp chain conveyor. The turning rolls may be moved vertically to permit an operator to manually rotate the workpiece about its longitudinal axis to a position determined by the operator to be the optimal position. The turning rolls are then lowered so that the workpiece re-engages the sharp teeth of the sharp chain conveyor for transport of the workpiece downstream through a scanner. An optimizer then determines an optimal cutting solution for the workpiece to produce the highest value or yield of lumber.
The manual rotation of the workpiece is a slow and time consuming process as the operator requires time to assess and position the workpiece in the most favorable position. Furthermore, such process may significantly reduce lumber recovery since the positioning of the workpiece by the operator is subject to human error in judgment. Once the operator lowers the workpiece back onto the sharp chain conveyor and the workpiece is transported downstream past the turning rolls, there is no means for repositioning the workpiece. If the operator incorrectly positioned the workpiece such error may compromise the optimal cutting solution determined by the scanner and optimizer, thereby reducing lumber recovery and there is no means of readjusting to correct the position of the workpiece.
To address the shortcomings of the SLI system, a “double Length Infeed” (DLI) system has been developed to eliminate the manual rotation of the workpiece. In place of the operator and turning rolls, the DLI system uses a scanner and optimizer to determine the optimal position of the workpiece and simultaneously, a rotating conveyor rotates the workpiece into such optimized position, thereby eliminating the time required to visually assess and manually rotate the workpiece. The workpiece is then fed onto a second conveyor where it passes through a second scanner and optimizer to determine the optimized cutting solution for the workpiece. On such a second conveyor, the workpiece may be further displaced laterally and angularly relative to its centreline so that the workpiece may be optimally positioned for processing in accordance with the optimized cutting solution. Once the workpiece is optimally positioned, it is fed onto a third conveyor, which is a sharp chain conveyor, to be transported to the primary breakdown sawing machines.
Although the DLI system is capable of positioning the workpiece in its optimized position, the workpiece may be subsequently displaced from its position as the workpiece is transported towards the primary breakdown machines. For example, hold-down rolls which ride along the upper surface of the workpiece to hold the workpiece in place on the conveyor may engage protruding knots or other superficial irregularities on the workpiece surface. Contact with such rough surfaces between the hold-down rolls and protruding knots may result in a displacement of the workpiece from its optimized position.
Furthermore, the workpiece may also be displaced when the workpiece is transported between the multiple conveyors. Distances between successive conveyors may span up to 40 inches and the workpiece may be transported butt first from conveyor to conveyor. Such a butt end, which is typically flared, may initially displace vertically downwards into the unsupported space defined by the span distance and be abruptly raised back onto the conveyor by engaging the succeeding conveyor, thereby disrupting the optimized position of the workpiece. Vertical rolls positioned between the conveyors to grip the workpiece and prevent it from displacing vertically into the void may be provided. However, such rolls may cause undesired movement of the workpiece as well. In addition, because of the length of the DLI system, substantial physical space is required to accommodate such machinery, thereby increasing the cost of production.
Accordingly, there is required a shorter conveyor system capable of positioning and maintaining the optimized position of a workpiece as the workpiece is being transported towards the primary breakdown machines.